Emulsion polymerization of certain vinyl compounds using a mercaptan modifier, a hydroperoxide catalyst, and oxygen



Patented Oct. 2, 1951 NT OFFICE EMULSION POLYMERIZATION OF CERTAIN VINYLCOMPOUNDS USING A MEROAPTAN MODIFIER, A HYDROPEROXIDE LYST, AND OXYGENEdwin J. Vandenberg, Wilmington, Del., asaignor to Hercules PowderCompany, Wilmington, Del., a corporation of Delaware No Drawing.Application June 17, 1848,

Serial No. 877,405

17 Claims. (01. 26082-5) This invention relates to the polymerization ofunsaturated organic compounds and, more particularly, to a method ofaccelerating by means of oxygen the polymerization of certain unsat-'urated organic compounds when these compounds are polymerized in aqueousemulsion.

It is well known that unsaturated organic compounds may be polymerizedin aqueous emulsion, in solution, and in the bulk. The eiiect of oxygenon such polymerizations has been studied, and it is known that oxygenmay exert either a beneficial or a detrimental efiect upon thepolymerizations, depending upon the type of monomer and the type ofcatalyst utilized. In the bulk photopolymerization of methylmethacrylate, for instance. it is known that the presence of oxygeninhibits the polymerization, since the rate of peroxide formationexceeds the rate of polymerization. Contrarily, it is known that air oroxygen markedly accelerates the bulk polymerization oi chloroprene.Relative to emulsion polymerization systems, it has been latelydiscovered that in the presence of the catalysts generally known to theart, for example, sodium perborate, benzoyl peroxide, barium peroxide,hydrogen peroxide, and the like, the polymerization of certain monomersis inhibited by the presence of oxygen.

Now, in accordance with this invention, it has been found that theemulsion polymerization or copolymerization of styrenes, coniugatedbutadiene hydrocarbons, and halogen-substituted conjugated butadienehydrocarbons, and the emulsion copolymerization of these compounds withother compounds containing the CH2=CH- group in the presence of amercaptan modifier and an organic hydroperoxide catalyst may beaccelerated by carrying out the polymerization or copolymerization inthe presence of up to about 0.4 oxygen, based upon the monomers.

In carrying out the process in accordance with ly mentioned may bepolymerized in the usual manner utilizing the well-known emulsiontechnique, 'with .the'exceptions that the catalyst utilized constitutesan organic hydroperoxide, such as an -u,a-dialkylarylmethylhydroperoxide, and

that the prescribed amount of oxygen is included in the. reactionvessel. Furthermore, it is necessary thata mercaptan modifier bepresent. By

the combination of such a modifienthe prescribed catalysts and thenecessary amount of oxygen,

polymerizations may be carried out at lower temperatures and in shorterreaction imes, and re- I 66 'Tlieprocedureoi suitin in higher yields.

CATA- The iollowing exa'mples are illustrative of the preparation ofpolymers by emulsion polymerizathis invention, the monomeric materialspreviousperiod of 48 hours. I yield of polymerwasobtained.

tion, and the products thereof, in accordance with this invention. Allparts given in the examples represent parts by weight.

Example 1 A glass polymerization vessel was charged with 41.! parts of a6% solution of the sodium salt of a dehydrogenated rosin (dehydroabieticacid 53%, abietic acid 0.0%, retene 0.2%), this solution containing 2.5parts of the sodium salt of the dehydrozenated rosin. To this solutionwere added 0.0841 part of -dimethylbenzyl hydroperoxide, 49.88 parts ofwater, 1.00 part of an activating salt solution, 0.25 part 01' laurylmercaptan, and 50'parts of styrene at a temperature of 25 C. The 1.00part of activating salt solution contained 0.00525 part of 78% ferricsulfate The emulsion was then run into an open vessel containing 5 partsof a 2% solution of phenyl-pnaphthylamine, stripped of the excessstyrene, and the polymer precipitated by the addition of an excess of asaturated salt solution. The precipitated polymer was washed with wateruntil alkali-free, then with alcohol, and finally was dried in anoven.A'93.8% yield of polystyrene was obtained.

A similar polymerization was carried out using the same proportions ofingredients except for the oxygen. The latter was supplied in the formof pure oxygen and in an' amount sufllcient to provide 0.2 part forevery'50 parts of (styrene. By this procedure,a yield of polystyrene wasobtained. w 1

ExampZe'Z Twelve and one-half parts of styrene and 87.5 parts ofisoprene were 'copolymerized according to the process of Example 1, inwhich 0.025 part of oxygen was introduced, utilizing a reaction Bythisprocedure, an 80.6%

raapieiwaat mawm 0.025 part of oxygen. with the substitution of 50 partsof butadiene-1.3 for the styrene previously shown. A 96.4% yield ofpolymer was obtained.

A similar polymerization was eil'ected using the same proportions ofingredients except for the oxygen. The latter was supplied in the formof pure oxygen and in an amount sumcient to Provide 0.2 part for every50 parts of butadiene-1,3. An 83% yield of polymer was obtained.

Example 4 Twelve and one-half parts of acrylonitrile and 37.5 parts ofbutadiene-1,3 were copolymerized following the process of Example 1,using 0.025 part of oxygen, with the exception that the polymerizationwas carried out for 18 hours. A 100% yield of polymer was obtained.

Example 5 A glass polymerization vessel was charged with 41.7 parts ofthe emulsifying solution of Example 1. To this soap solution were added0.15 part of potassium persulfate dissolved in 25 parts of water, 0.0171part of s,-dimethylbenzyl hydroperoxide, 24.88 parts of water, 1.00 partof the activating salt solution of Example 1, 12.5 parts of styrene,0.25 part of lauryl mercaptan, and 37.5 parts of butadiene-L3. All ofthe charging operations were carried out at a temperature of 25 0.,

after which the reaction vessel was sealed. and its contents frozen bycooling. The vessel then was opened and the free space thoroughly sweptout with air. resulting in the introduction of 0.025 part of oxygen,based on the monomers, after which the vessel again was sealed and thereaction 'mixture agitated at 40" C. for 25 hours. The emulsion was thenrun into an open vessel containing 5 parts of a 2% solution ofphenyl-pnaphthylamine, stripped of the excess butadiene, and the polymerprecipitated by the addition of an excess of a saturated salt solution.The precipitated polymer was washed with water until alkali-free, thenwith alcohol, and finally was Example 7 The general procedure of Example5 was followed, using 0.057 part of t-butyl hydroperoxide in place ofthe ,-dimethylbenzyl hydroperoxide, and sweeping out the reaction vesselwith air so as to introduce 0.025 part of oxygen. The

polymerization was carried out for 16 hours. re-

sulting in a 79.4% yield. When the Polymerization was carried out for 22hours, a 96.4% yield was obtained.

Example 8 The general procedure of Example 5 was followed, using 2.5parts of a fatty acid soap'(sodium salt 1 of a mixture of palmitic andstearic acids), and a mixture of oxygen and nitrogen to sweep out thefree space in the reaction vessel. The oxygen-nitrogen mixture was somade up to result in the addition of 0.006 part of oxygen. A reactionperiod of 7 hours resulted in a 69% yield of polymer. Under identicalconditions, with the exception that 0.0125 part of oxygen wasintroduced, a 73% yield resulted. Likewise, 0.025 part of oxygen gave a76% yield.

Following the above procedure, using 2.5 parts of sodium laurate as theemulsifying agent and 0.025 part of oxygen, a 91% yield of polymer wasobtained in 11 hours. In- 16 hours. the yield was Example 9 Apolymerization similar to that in Example 1 was carried out using 0.1072part of a-dimethyl p-isopropylbenzyl hydroperoxide in place of thea,a-dimethylbenzyl hydroperoxide, and utilizing 0.2 part of oxygen, theremaining ingredients being in the same proportions as in Example 1. A100% yield of polystyrene was obtained.

Example 10 The procedure of Example 9 was followed with the exceptionthat 0.0911 part of a,a-dimethylp-methylbenzyl hydroperoxide was used inplace of the a,a-dimethyl-p-isopropylbenzyl hydroperoxide. A 100% yieldof polystyrene resulted.

Example 11 A glass polymerization vessel was charged with 41.7 parts ofthe emulsifying solution of Example 1. To this soap solution were added0.085 part of ,a-dimethylbenzyl hydroperoxide, 41.6 parts of water, 10parts of the activating salt solution of Example 1, 12.5 parts of methylmethacrylate, 0.25 part of lauryl mercaptan, and 37.5 parts ofbutadiene-1,3. All of the charging operations were carried out at atemperature of 25 0., after which the reaction vessel was sealed, andits contents frozen by cooling. The vessel then was opened and the freespace thoroughly swept out with air, resulting in the introduction of0.025 part of oxygen, based on the monomers, after which the vesselagain was sealed and the reaction mixture agitated at 40 C. for 40hours. Upon working up the reaction mixture as in Example 1 a 92% yieldof copolymer was obtained.

The organic hydroperoxides which are operable in this invention havebeen illustrated by the examples with the use of,a-dimethyl-pmethylbenzyl, a,-dimethylbenzyl,a,a-dimethylp-isopropylbenzyl, and t-butyl hydroperoxides.

Other alkyl hydroperoxides corresponding to the t-butyl hydroperoxide,such as t-amyl hydroperoxide, also are operable in accordance with thisinvention. The a,-dialkylarylmethyl hydroperoxides used in the processof this invention may be prepared by the oxidation of alkylsubstitutedaromatic compounds having the structural formula in which R1 and R:represent alkyl groups and Ar represents a substituent selected from thegroup consisting of aryl and substituted aryl groups. The oxidation maybe carried out in the liquid phase utilizing air or molecular oxygen asthe oxidizing agents. A preferred methodof preparing thesehydroperoxides involves the liquid phase oxidation of thealkyl-substituted aromatic organic compounds having the above structuralformula by passing an oxygencontaining gas through the compounds at atemperature between about 25 C. and about 95 C. in the presence of anaqueous alkali. The concentration of the aqueous alkali may be betweenabout 1% and about 35%, although it is preferable to use concentrationsof about 2% to about 8%. Vigorous agitation is desirable during theoxidation reaction.

As illustrative of the alkyl-substituted aromatic organic compoundswhich may be oxi dized, p-cymene, cumene, and diisopropyl benzene may bementioned. These compounds lead to a,a-dimethyl-p-methylbenzyl,a,a-dimethylbenzyl, and a,a-dimethyl-p-isopropylbenzyl hydroperoxides,respectively. The aryl and substituted aryl groups need not be derivedfrom benzene, as is the case in the afore-mentioned compounds-forcompounds containing aromatic nuclei derived from naphthalene,anthracene, phenanthrene, and the like, also are operable when dissolvedin a suitable solvent during the oxidation. The aryl group may besubstituted with alkyl groups such as methyl, ethyl, propyl, isopropyl,butyl, isobutyl, tertiary butyl, and the like to give alkarylsubstituents, the same alkyl groups also being representative of R1 andR2 such as the hydroxide or carbonate of sodium or potassium. Thedehydrogenated rosins are prepared by the dehydrogenation ordisproportionation of natural rosin or a rosin material containing asubstantial amount of a natural rosin. The dehydrogenation ordisproportionation reaction is carried out by contacting the rosin orrosin material at an elevated temperature with an active hydrogenationcatalyst in the absence of added hydrogen. Catalyst such as palladium,platinum, nickel. and copper chromite are suitable and may be supportedon a carrier such as granular alumina, fibrous asbestos or activatedcharcoal. The catalytic treatment may be conducted either by a batchwiseor continuous procedure. The rosin may be agitated, for example, withabout 5% to about 20% by weight of a palladium catalyst supported onactivated carbon (1% to 2% palladium) at about 150 C. to about 300 C.for about 1 hour to about 5 hours. In the continuous process the moltenrosin flows over a supported palladium catalyst at a temperature withinthe range of about 225 C. to about 300 C. to provide a contact time ofabout hour to about 1 hour.

It often is advantageous to refine the whole rosinprior to itsdehydrogenation or disproportionation and the same is true as applied tothe whole dehydrogenated or disproportionated The preferable amount ofhydrop'eroxide on this basis, however, is from about 2% to about 9%, anda particularly applicable amount is from about 2% to about 5%. When, asin Example 6, a watersoluble persulfate is used in conjunction with thehydroperoxide to catalyze the polymerization, the amount ofhydroperoxide may be considerably less than when no persulfate ispresent. Under such circumstances, the

, amount of hydroperoxide may range from about 0.5% to about 2%, aparticularly applicable amount being about 1%.

The process of this invention may be carried out using variousemukifying agents, such as fatty acid soaps; the water-soluble salts ofhydrogenated anddehydrogenated rosins or the pure acids thereof, such asdihydroabietic, tetrahydroabietic and dehydroabietic acids; thewater-soluble salts of the amines derived from hydrogenated anddehydrogenated rosins or the pure acids thereof, for example, theacetates of dihydroabietylamine, tetrahydroabietylamine, anddehydroabietylamine; and any other emulsifying agent well known in theart. The rosin amines mentioned may be prepared by converting the acidsin the rosin material to the corresponding nitriles by treatment withammonia under dehydrating conditions, and then reducing the nitrilestothe amines by catalytic hydroenation.

Most of the examples, however, have shown the use of a salt of adehydrogenated rosin as emulsifying agent. Such salts are prepared byproduct. Prior to its dehydrogenation or disproportionation the rosinmay be refined by crystallization, by means of a selective solvent suchas furfural or phenol, or by an absorbent earth such as fullers earth.The dehydrogenated or disproportionated rosin product may be refined bydistillation, heat-treatment, alkali extraction, precipitation, etc. Itis desirable that the dehydrogenated or disproportionated rosin orderiva-- tive thereof contain at least 45% and preferably at least 50%dehydroabietic acid. The dehydrog'enated or disproportionatedrosin alsoshould contain less than 1% abietic acid.

The examples have shown the use of air and oxygen and of mixtures ofoxygen and nitrogen as the source of the oxygen used in accordance withthis invention, but mixtures of oxygen with other inert gases and of airwith an inert gas such as nitrogen are operable. It is desirable thatoxygen be the only oxygen-yielding gas present. The amount of oxygen maybe varied up'to about 0.4%, based on the monomers. The beneficial effectof oxygen is most noticeable in the range from about 0.01% to about 0.4and a preferable range is from about 0.05% to about 0.2%.

As shown by the examples, various activating salts may be added to thepolymerization reaction mixture. The activating salts shown'by theexamples; namely, ferric sulfate, sodium pyrophosphate, and cobaltouschloride, constitute a redox system, which is so called because of itsproperty of catalyzing oxidation-reduction reactions. Such systemsusually comprise a salt of a heavy metal, such as iron, cobalt, ornickel associated with a complex-forming compound, such as apyrophosphate. The redox system, therefore, comprises essentially aheavy metal complex wherein the metal is united to another elementthrough coordinate convalences rather than primary valences. Amountsbetween about 0.1% and about 2% by weight of the heavy metal complexes,based on the monomers present, may be used, and amounts betweenabout.0.1% and about aucauoc 1% by weight are generally suitable. Thesalts of some heavy metals, such as iron, are sufficiently active sothat the salt of only one metal need be present, but usually the redoxsystem contains at least two heavy metal salts, and each individual saltmay be present in the redox system in amounts between about 0.0003% andabout 0.1% by weight, based on the monomers employed, though amountsbetween about 0.0003% and about 0.01% by weight are generallysufiicient.

Compounds which may be advantageouslypolymerized in aqueous emulsion inaccordance with this invention include the styrenes, such as styrene,a-methyl styrene, p-methyl styrene,

polymerized individually or copolymerized with one another. The abovecompoundsalso may be copolymerized with another compound containing theCHz='CH-, or vinyLgroup, such as acrylonitrile, methyl acrylate, methylmethacrylate, methyl vinyl ketone, methyl isopropenyl ketone, etc.Copolymer systems involving from two to four difierent monomers may beutilized,

but an even greater number of monomers would be operable. I

The polymerizations may be carried out under conditions well-known inthe art for emulsion polymerization; e. g., concentration of reactants,temperature, pressure, etc. The temperature of the polymerizationreaction may vary from about C. to about 100 C., and the concentrationof the emulsifying, agent in the aqueous phase may be varied from about1% to-about 5%, preferably from about 2% to about 3%. During thepolymerizations, it is necessary that a mercaptan modifier be present.,All of the mercaptan modifiers well known to the art, such as laurylmercaptan, are operable. v

When used in conjunction with a mercaptan modifier andthe prescribedamount of oxygen, the organic hydroperoxide catalysts of this inven tlonpermit a higher yield of polymer under the same conditions than do thecatalysts as previously used in the art. By this-invention, the timerequired to obtain a given yield of polymer is reduced as compared toprevious processes, thereby increasing the capacity of a polymerizationvessel and decreasing the cost of the polymer. Furthermore, throughpractice of this invention, increased yields are obtained bypolymerizations carried out at lower temperatures for periods 01' timecomparable ,to those which have been previously used.

The process 01' this invention as used in the preparation of rubberlikepolymers does not materially change the properties ofsuch polymers asthey have been recognized before. The process also is very applicable topolymerizations carried out with soaps of dehydrogenated rosin asemulsii'ying agents. It is known that dehydrogenated rosin soaps impartdesirable physical properties to rubberlike polymers, such as thosederived from the copolymerization of butadiene and styrene, but the useof these soaps has been somewhat disadvantageous due to the fact thatthey necessitated longer reaction periods than did fatty acid soaps. Theprocess of this invention permits the use of dehydrogenated rosin soapsto obtain in comparable lengths of time polymer yields which 8 r areequivalent to those obtained under previously utilized conditions withfatty acid soaps as emulsifying agents.

What I claim and desire to protect by Letters Patent is: i

1. The process which comprises polymerizing in aqueous emulsion at leastone monomeric organic compound of the group consisting of a styrene, aconjugated butadiene hydrocarbon and a halogen-substituted conjugatedbutadiene hydrocarbon, in the presence of an alkyl mercaptan modifier,an organic hydroperoxide catalyst, and

an amount of oxygen from'0.01% to 0.4%, based on the monomer.v

2. The process which comprises copolymerizing in aqueous emulsion atleast one monomeric organic compound of the group consisting of astyrene, a conjugated butadiene hydrocarbon and a halogen-substitutedconjugated butadiene hydrocarbon with another organic compoundcontaining the CHz='CH-group, in the presence of an alkyl mercaptanmodifier, an organic hydroperoxide catalyst, and an amount of oxygenfrom 0.01% to 0.4%,.based on the monomer.

3. The process which comprises polymerizing in aqueous emulsion atleastone monomeric organic compound of the groupconsisting of a styrene,a conjugated butadiene hydrocarbon and a halogensubstltuted conjugatedbutadiene hydrocarbon, in the presence of an alkyl mercaptan'modifier,an organic hydroperoxide catalyst, an activator comprising awater-soluble pyrophosphate and watersolube salts of two heavy metalsselected from thegroup consisting of iron, cobalt and nickel, and anamount of oxygen from 0.01% to 0.4%, based on the monomer.

4. The process which comprises polymerizing in aqueous emulsion at leastone monomeric organic compound of the group consisting of a styrene, aconjugated butadiene hydrocarbon and a halogen-substituted conjugatedbutadiene hydrocarbon, in the presence oi' an alkyl mercaptan modifier,an organic hydroperoxide catalyst, an activator comprising awater-soluble pyrophosphate and water-soluble salts of iron and cobalt,and an amount of oxygen from 0.01% to 0.4%, based on the monomer.

5. Theprocess which comprises polymerizing in aqueous emulsion at leastone monomeric organic compound of the group consisting of a styrene, aconjugated butadiene hydrocarbon and a halogen-substituted conjugatedbutadiene hydrocarbon, in the presence of an alkyl mercaptan modifier,an organic hydroperoxide catalyst, an activator comprising sodiumpyrophosphate, ferric sulfate and colbaltous chloride, and an amount ofoxy en from 0.01 to 0.4%, based on the monomer.

6. The process which comprises polymerizing in aqueous emulsion at leastone monomeric organic compound of the group consisting of a styrene, aconjugated butadiene hydrocarbon and a halogen-substituted conjugatedbutadiene hydrocarbon, in the presence of an alkyl mercaptan modifier,an organic hydroperoxide catalyst, and an amount of oxygen from 0.05% to0.2%, based on the monomer.

hydroperoxide catalyst, and an amount of oxygen from 0.01% to 0.4%,based on the monomer.

11. The process which comprises co'polymerizing-in aqueous emulsionbutadiene-1,3 and styrene in the presence of lauryl mercaptan as amodifier, t-butyl hydroperoxide as a catalyst, and an amount of oxygenfrom 0.01% to 0.4%,based on the monomers.

12. The process which comprises copolymerizing in aqueous emulsionbutadiene-1,3 and acrylonitrile in the presence of lauryl mercaptan as amodifier, t-amyl hydroperoxide as a catalyst, and an amount of oxygenfrom 0.01% to 0.4%, based on the monomers.

13. The process which comprises copolymerizing in aqueous emulsionbutadiene-1,3 and styrene in the presence of lauryl mercaptan as amodifier, t-butyl hydroperoxide as a catalyst, an

activator comprising sodium pyrophosphate, ferric sulfate and cobaltouschloride, and 0.1% of oxygen, based on the monomers.

14. The process which comprises copolymerizing in aqueous emulsionbutadiene-l,3 and styrene in the presence of an alkyl mercaptanmodifier, an a,u-dialkylarylmethy1 hydroperoxide as a catalyst, and anamount of oxygen from 0.01% to 0.4%, based on the monomers.

15. The process which comprises copolymerizing in aqueous emulsionbutadiene-LS and acrylom'trile in the presence of an alkyl mercaptanmodifier, an a,a-dialkylarylmethyl hydroperoxide as a catalyst, and anamount of oxygen from 0.01% to 0.4%, based on the monomers.

16. The process which comprises copolymerlzing in aqueous emulsionbutadiene-l,3 and styrene in the presence of lauryl mercaptan as amodifier, an a,u-dimethylbenzyl hydroperoxide as a catalyst, and anamount of oxygen from 0.01% to 0.4%, based on the monomers.

17. The process which comprises copolymerizing in aqueous emulsionbutadiene-1,3 and acrylonitrile in the presence of lauryl mercaptan as amodifier, an a,a-dimethylbenzyl hydroperoxide as a catalyst, and anamount of oxygen from 0.01% to 0.4% based on the monomers.

EDWIN J. VANDENBERG.

REFERENCES CITED The vfollowing references are of record in the

1. THE PROCESS WHICH COMPRISES POLYMERIZING IN AQUEOUS EMULSION AT LEASTONE MONOMERIC ORGANIC COMPOUND OF THE GROUP CONSISTING OF A STYRENE, ACONJUGATED BUTADIENE HYDROCARBON AND A HALOGEN-SUBSTITUTED CONJUGATEDBUTADIENE HYDROCARBON, IN THE PRESENCE OF AN ALKYL MERCAPTAN MODIFIER,AN ORGANIC HYDROPEROXIDE CATALYST, AND AN AMOUNT OF OXYGEN FROM 0.01% TO0.4%, BASED ON THE MONOMER.